The present invention relates to a gasoline engine having direct fuel injection.
In internal combustion engines with direct fuel injection, a combustion chamber is delimited in each cylinder by a longitudinally movable piston and the inner wall of a cylinder head, with an injector injecting fuel into the combustion chamber to produce a mixture internally with separately supplied combustion air. The composition of the fuel/air mixture must be within the ignitable window in order to be ignitable using an ignition spark which can be triggered between the electrodes of a spark plug.
An internal combustion engine having direct fuel injection is described in European Published Patent Application No. 0 835 994. The internal combustion engine includes a combustion chamber having a pent-roof shape, a centrally located injector, and electrodes of the spark plug located near an admission valve. The fuel is injected in the form of a hollow cone into a piston having a cavity with a circular projecting part and strikes against the piston cavity. The fuel scattered in this manner is transported by a tumble current to the electrodes of the spark plug, the circular projecting part of the piston trough preventing the atomized fuel from being scattered in the direction of the cylinder wall, thus ensuring a stable stratified charge combustion.
An internal combustion engine having direct fuel injection is described in German Published Patent Application No. 195 46 945, the injectors of which inject the fuel in a cone shape into the combustion chamber with their injection nozzles, with the spark plug being positioned in such a way that its electrodes are outside the lateral surface of the conical fuel jet produced by the injection nozzle. In this manner, wetting of the electrodes with fuel during the injection process is avoided and carbon black deposition on the electrodes due to incompletely combusted fuel is counteracted. The electrodes are free of coking over a long period of operation, which should ensure proper operation of the internal combustion engine without misfires. In order to bring ignitable mixture between the electrodes positioned outside the conical fuel jet, the spark plug is positioned so that the ground electrode is at a small distance from the lateral surface of the conical fuel jet and the inner wall of the cylinder head runs extends parallel to the lateral surface of the conical fuel jet while forming a gap at least at the location where the electrodes of the spark plug are positioned.
A turbulent flow composed of fuel/air mixture and extends into the region of the electrodes is to result in the gap. In order to generate the turbulent flow, the inner wall must be specially shaped and the spark plug must be positioned near the injector. The injector is located in a counter borehole of the inner wall, i.e., set back from the free combustion chamber volume, which should cause the mixture vortex to arise in the region adjacent to the injection nozzle and to circulate in the hollow space which is formed between the lateral surface of the conical fuel jet and the inner wall of the cylinder head in the region of the injection nozzle. Furthermore, air displaced by the fuel injected into the combustion chamber is to flow back through the air gap between the conical fuel jet and the parallel inner wall of the cylinder head, which is also conical. As the air flows back toward the spark plug along the inner wall, further fuel particles from the conical fuel jet are to be entrained. The turbulent flow is implemented sufficiently strongly in the region near the injector to bring ignitable mixture between the electrodes of a spark plug. Therefore, the spark plug must be located near the injector.
In a convention gasoline engine having direct fuel injection, the combustion chamber perimeter, particularly that formed by the inner wall of the cylinder head, must be precisely configured at high expense to achieve the desired hydromechanical effects for forming the ignitable mixture vortices. The conventional combustion chamber configuration having the combustion chamber shape necessary for mixture vortex formation and the unavoidable location of the spark plug near the injector often cannot achieve optimal combustion and ensure the desired operating behavior of the internal combustion engine.
It is an object of the present invention to provide a gasoline engine having direct fuel injection so that the internal combustion engine functions with optimal operating behavior.
In the combustion chamber configuration according to the present invention, the conical fuel jet is injected in a free jet which is substantially uninfluenced by the combustion chamber perimeter, i.e., the conical fuel jet is injected at a sufficiently great distance, particularly from the inner wall of the cylinder head, that the conical fuel jet expands in the free combustion chamber volume substantially without hydromechanical wall effects of the combustion chamber perimeter. At the same time, fuel vortices, which arise from the lateral surface of the conical jet, are formed during the injection, initially substantially composed of fuel vapor and mixing with the surrounding combustion air in the combustion chamber. The fuel vortices develop particularly distinctly if the opening angle of the conical fuel jet is between 70xc2x0 and 100xc2x0 and are generated by an air stream which arises in the region of the lateral surface of the conical fuel jet due to the air entrained by the fuel jet, with an air current also being generated in the opposite direction by the resulting partial vacuum. According to the present invention, the spark plugs are positioned so that the electrodes project into the fuel vortex of the free jet. The spark position of the electrodes may be at a distance of 1 mm to 15 mm from the lateral surface of the conical fuel jet.
The fuel vortex which brings ignitable mixture between the electrodes develops on the lateral surface of the free jet without effective influence of the combustion chamber perimeter, so that the shape of the combustion chamber may be designed freely. A jet-guided combustion process is present, in which wall effects of the inner wall of the cylinder head or, for example, a piston cavity, exercise hardly any influence on the formation of the mixture and the ignition. Particularly in the stratified charge operation of the internal combustion engine, when fuel injection occurs during the compression stroke and a central fuel cloud is formed in the air-filled combustion chamber, an optimal burn-through of the combustion chamber charge may be achieved with a simple combustion chamber configuration. A further advantage of the mixture formation according to the present invention is that the spark plug may be located further from the injector. The fuel vortex stably remains at the same location in the combustion chamber for a long time, so that the ignition may occur within a broad time interval, independently from the time of injection.
The free jet of fuel may be injected into the combustion chamber in the shape of a hollow cone. In this manner, the fuel vortices form in a shape particularly suitable for conveyance of mixture to the spark plug, particularly for injection at a high cylinder pressure in the compression phase during stratified charge operation. The conical fuel jet may be implemented with the shape of a hollow cone particularly easily if the injector has an injection nozzle which opens outwardly.